suddenly, after a power shutdown, the web interface is no more reachable, but everything seems to work (it happened 3 weeeks ago and no one noticed). what have I to check via shell? Is it possible, via shell, to make a backup and restore it after a fresh installation?
Go to the ZS console and select Z (Fasilsafe mode). I think this will restart your installation to use the temporary profile, and from there you could log on to the web interface at the default IP (192.168.0.75) and take a backup of your profile. You could then restore it to a fresh installation.
You could also use D (Profile Manager) on the console to deactivate the active profile and restart, which would do a similar thing, but it would stay in the temporary profile until you back up / restore your original profile.
Both of these approaches would take your router offline, so you’d cut off your normal client PCs while you did this. Also, I don’t know what would happen if you tried restoring a possibly corrupted profile.